I wanted to try and show how i think when setting up multiple lights in a scene.
The image above is lit with 3 SB900 flash guns. Including the stand lamp :0)
I wanted to see if any of the lights in the room are effecting the scene. Here is a shot with my flashes turned off. At F6.3 1/125sec iso 200 there are no external lights influencing the shot.
Now shooting in Manual, you keep the settings locked in and just change the lighting. All these shots have the same aperture, shutter speed and iso settings.
Here i have a strobe placed in the lamp shade. I turned it to a power where it will not blow out and so some detail will remain.
Here i have one light one, in a soft box lighting in the direction of the arrow. Its set to lift some of the shadows that are created.
Lastly i used a strobe high up with a grid on the front to create some directional light.
To set each light you have to add them one at a time. Even when happy with a light, turn it off so that you can see how the next light will effect the shot. Once happy turn on and have some fun.